Hybrid inorganic-organic host-guest compounds: open-framework cadmium oxalates incorporating novel extended structures of alkali halides

Abstract

Four unusual inorganic-organic nanocomposites containing extended alkali halide structures, present as layers or as three-dimensional units, have been synthesized by a metathetic reaction carried out under hydrothermal conditions. These compounds, with cadmium oxalate host lattices and the alkali halide structures as guests, have the compositions [RbCl][Cd₆(C₂O₄) ₆]·2H₂O, I; 2[CsBr][Cd(C₂O₄)]·H₂O, II; 2[CsBr][Cd₂(C₂O₄)(Br)₂]·2H₂O, III; and 3[RbCl][Cd₂(C₂O₄)(Cl₂)]·H₂O, IV. Crystal data for I, rhombohedral, space group = R-3 (no. 148), a = 9.3859(3), c = 23.9086(8) Å; V = 1824.05(1) ų, Z = 18, M = 1359.51, ρ_calcd = 3.702 g cm^-3, μ(Mo Kα) = 7.375 mm^-1, R₁ = 0.04, wR₂ = 0.0904 [537 observed reflections with I > 2σ(I)]; for II, orthorhombic, space group = Pbcm (no. 57), a = 6.0854(6), b = 11.0793(11), c = 16.889(2) Å; V = 1138.7(2) ų, Z = 8, M = 644.06, ρ_calcd = 3.745 g cm^-3, μ(Mo Kμ) = 15.219 mm^-1, R₁ = 0.04, wR₂ = 0.08 [408 observed reflections with I > 2σ(I)]; for III, orthorhombic, space group = Cmcm (no.63), a = 23.6151(14), b = 10.2528(6), c = 7.8199(6) Å; V = 1894.2(2) ų, Z = 16, M = 970.33, ρ_calcd = 3.374 g cm^-3, μ(Mo Kα) = 14.487 mm^-1, R₁ = 0.03, wR₂ = 0.0744 [651 observed reflections with I > 2σ(I)]; for IV, monoclinic, space group = P2₁/c (no. 14), a = 8.0648(2)(3), b = 22.9026(4), c = 9.3967(3) Å; V = 1681.10(7) ų, Z = 4, M = 782.53, ρ_calcd = 3.076 g cm^-3, μ(Mo Kα) = 11.961 mm^-1, R₁ = 0.04, wR₂ = 0.093 [2071 observed reflections with I > 2σ(I)]. Compounds I-IV possess many unusual structural features. While I has interpenetrating lattices of the three-dimensional cadmium oxalate and RbCl with an expanded lattice, giving rise to a super rock-salt cell, II possesses alternating cadmium oxalate and CsBr layers, the latter comprising six-membered CsBr rings. Compounds III and IV have isolated cadmium oxalate units (zero-dimensional) linked and stabilized by the alkali halides.